The present invention relates to a novel method for producing a compound of the formula [XVI]
wherein Me is methyl, Bu-t is t-butyl and Ph is phenyl, which is useful as a treatment drug of HIV-related diseases based on its inhibitory action on proteases derived from viruses, various novel intermediates useful for producing said compound [XVI], and to the method for production of the intermediates. These intermediates can be used for not only production of the above-mentioned compound [XVI] but also for production of various compounds.
The above-mentioned compound [XVI] useful as an HIV protease inhibitor is known as described in WO95/09843. This compound [XVI] has been conventionally produced from serine as a starting material, by increasing carbon and numerous other steps inclusive of stereoselective reduction of carbonyl group. Such conventional production method is extremely complicated and inefficient, since it requires expensive starting materials and constant low temperature conditions for reactions. Accordingly, there remain many problems to be solved before the conventional synthetic method is actually put to industrial practice.
In addition, 2,2-dimethyl-6-amino-1,3-dioxepan-5-ol which is described, for example, in U.S. Pat. No. 4,439,613 is an intermediate for producing a compound useful as an X ray contrast medium, and even though the compound obtained is a racemate, resolution of the racemate itself by a method such as recrystallization has been extremely difficult. Moreover, this U.S. patent does not suggest production of specific enantiomers of the present invention.
Accordingly, an object of the present invention is to provide a method for stereoselectively and extremely efficiently producing the above-mentioned compound [XVI] useful as an HIV protease inhibitor upon solution of the above-mentioned problems. Another object of the present invention is to provide a novel intermediate useful for producing said compound and a production method thereof.
The present inventors have made intensive studies in an attempt to achieve the above-mentioned objects, and found that a step comprising acetalating or ketalating (z)-2-butene-1,4-diol, and epoxidation of the obtained compound to give a 3,5,8-trioxabicyclo[5.1.0]octane derivative, which is followed by an epoxy ring-opening reaction using a chiral amine, leads to a stereospecific (5R, 6S)-6-substituted amino-1,3-dioxepan-5-ol derivative or an enantiomer thereof, from which a compound of the following formula [XV], that is, a compound inclusive of the aforementioned compound [XVI] useful as an HIV protease inhibitor, can be extremely efficiently produced stereoselectively through various other steps, which resulted in the completion of the present invention.
Thus, the present invention provides the following (1) to (15).
(1) A (5R, 6S)-6-substituted amino-1,3-dioxepan-5-ol derivative of the formula [V]
wherein R1 and R2 are the same or different and each is a hydrogen atom, an alkyl or an aryl, or R1 and R2 combinedly form a cycloalkyl ring together with the adjacent carbon atom, and R3 is an aralkylamine residue or amino acid derivative residue having an (R) or (S) configuration, an enantiomer thereof and a salt thereof.
(2) A method for producing a (5R,6S)-6-substituted amino-1,3-dioxepan-5-ol derivative of the formula [V]
wherein R1, R2 and R3 are as defined above, and an enantiomer thereof, comprising subjecting a 3,5,8-trioxabicyclo[5.1.0]octane derivative of the formula [III]
wherein R1 and R2 are as defined above, to an epoxy ring-opening reaction using a chiral amine of the formula [IV]
R3xe2x80x94NH2xe2x80x83xe2x80x83[IV]
wherein R3 is as defined above, and crystallizing a produced mixture of isomers.
(3) A (5R,6S)-6-amino-1,3-dioxepan-5-ol derivative of the formula [VI]
wherein R1 and R2 are as defined above, an enantiomer thereof and a salt thereof.
(4) A method for producing a (5R,6S)-6-amino-1,3-dioxepan-5-ol derivative of the formula [VI]
wherein R1 and R2 are as defined above, an enantiomer thereof and a salt thereof, comprising subjecting a 3,5,8-trioxabicyclo[5.1.0]octane derivative of the formula [III]
wherein R1 and R2 are as defined above, to an epoxy ring-opening reaction using a chiral amine of the formula [IV]
R3xe2x80x94NH2xe2x80x83xe2x80x83[IV]
wherein R3 is as defined above, and crystallizing a produced mixture of isomers to give a (5R,6S)-6-substituted amino-1,3-dioxepan-5-ol derivative of the formula [V]
wherein R1, R2 and R3 are as defined above, or an enantiomer thereof, and removing a substituent on an amino group of this compound to make the 6-position thereof a non-substituted amino group.
(5) An oxazoline derivative of the formula [X]
wherein R4 is an optionally substituted alkyl, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted aralkyl or an optionally substituted heteroarylalkyl, R5 is a hydrogen atom or an acyl, and Z is a substituent which functions as a leaving group together with an oxygen atom, an enantiomer thereof and a salt thereof.
(6) A method for producing an oxazoline derivative of the formula [X]
wherein R4, R5 and Z are as defined above, and an enantiomer thereof, comprising treating a 1,3-dioxepane derivative of the formula [IX]
wherein R1, R2, R4 and Z are as defined above, or an enantiomer thereof, with a Lewis acid to form an oxazoline ring, followed by acylation as necessary.
(7) A method for producing an oxazoline derivative of the formula [X]
wherein R4, R5 and Z are as defined above, and an enantiomer thereof, comprising reacting a (5R,6S)-6-amino-1,3-dioxepan-5-ol derivative of the formula [VI]
wherein R1 and R2 are as defined above, an enantiomer thereof or a salt thereof, with a reactive carboxylic acid derivative having R4 wherein R4 is as defined above, in the presence of a base, to give a (5R,6S)-6-acylamino-1,3-dioxepan-5-ol derivative of the formula [VIII]
wherein R1, R2 and R4 are as defined above, or an enantiomer thereof, reacting the resulting compound with a sulfonylating agent, treating the resulting compound with a Lewis acid, and acylating said compound, where necessary.
(8) An (oxazolin-4-yl)oxirane derivative of the formula [XI]
wherein R4 is as defined above, an enantiomer thereof and a salt thereof.
(9) A method for producing an (oxazolin-4-yl)oxirane derivative of the formula [XI]
wherein R4 is as defined above, and an enantiomer thereof, comprising treating, with a base, an oxazoline derivative of the formula [X]
wherein R4, R5 and Z are as defined above, or an enantiomer thereof.
(10) A method for producing an (oxazolin-4-yl)oxirane derivative of the formula [XI]
wherein R4 is as defined above, and an enantiomer thereof, comprising reacting a (5R,6S)-6-amino-1,3-dioxepan-5-olderivative of the formula [VI]
wherein R1 and R2 are as defined above, an enantiomer thereof or a salt thereof, with a reactive carboxylic acid derivative having R4 wherein R4 is as defined above, in the presence of a base, to give a (5R,6S)-6-acylamino-1,3-dioxepan-5-ol derivative of the formula [VIII]
wherein R1, R2 and R4 are as defined above, or an enantiomer thereof, reacting the resulting compound with a sulfonylating agent, treating the resulting compound with a Lewis acid, and acylating said compound, where necessary, to give an oxazoline derivative of the formula [X]
wherein R4, R5 and Z are as defined above, or an enantiomer thereof, and treating the obtained compound with a base.
(11) A 4-(2-amino-1-hydroxyethyl)oxazoline derivative of the formula [XIII]
wherein R4 is as defined above, and R6 and R7 are the same or different and each is a hydrogen atom, an optionally substituted alkyl, an optionally substituted aryl, an optionally substituted heteroaryl or an optionally substituted aralkyl, or R6 and R7 combinedly form, together with the adjacent nitrogen atom, a hetero ring, said hetero ring being optionally-substituted by halogen atom, alkyl, alkenyl, alkoxy, amino, alkoxycarbonyl, carboxamide or alkyl-substituted carbamoyl, an enantiomer thereof and a salt thereof.
(12) A method for producing a 4-(2-amino-1-hydroxyethyl)oxazoline derivative of the formula [XIII]
wherein R4, R6 and R7 are as defined above, and an enantiomer thereof, comprising reacting an (oxazolin-4-yl)oxyrane derivative of the formula [XI]
wherein R4 is as defined above, or an enantiomer thereof, with an amine of the formula [XII]
wherein R6 and R7 are as defined above.
(13) A method for producing a 4-(2-amino-1-hydroxyethyl)oxazoline derivative of the formula [XIII]
wherein R4, R6 and R7 are as defined above, and an enantiomer thereof, comprising treating an oxazoline derivative of the formula [X]
wherein R4, R5 and Z are as defined above, or an enantiomer thereof with a base to give an (oxazolin-4-yl)oxyrane derivative of the formula [XI]
wherein R4 is as defined above, or an enantiomer thereof, and reacting the resulting derivative [XI] with an amine of the formula [XII]
wherein R6 and R7 are as defined above.
(14) A method for producing an amide derivative of the formula [XV]
wherein R4, R6 and R7 are as defined above, and R8 is a hydrogen atom, an alkyl, an optionally substituted aryl or an optionally substituted aralkyl, and an enantiomer thereof, comprising subjecting a 4-(2-amino-1-hydroxyethyl)oxazoline derivative of the formula [XIII]
wherein R4, R6 and R7 are as defined above, or an enantiomer thereof to ring opening with a mercaptane of the formula [XIV]
xe2x80x83R8xe2x80x94SHxe2x80x83xe2x80x83[XIV]
wherein R8 is as defined above.
(15) A method for producing an amide derivative of the formula [XV]
wherein R4, R6, R7 and R8 are as defined above, and an enantiomer thereof, comprising reacting an (oxazolin-4-yl)oxirane derivative of the formula [XI]
wherein R4 is as defined above, or an enantiomer thereof, with an amine of the formula [XII]
wherein R6 and R7 are as defined above, to give a 4-(2-amino-1-hydroxyethyl)oxazoline derivative of the formula [XIII]
wherein R4, R6 and R7 are as defined above, or an enantiomer thereof, and subjecting this compound to ring opening with a mercaptane of the formula [XIV]
R8xe2x80x94SHxe2x80x83xe2x80x83[XIV]
wherein R8 is as defined above.
As used herein, alkyl may be linear or branched and preferably has 1 to 6 carbon atom(s). Specific examples thereof include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl, pentyl, isopentyl, neopentyl, t-pentyl, hexyl, isohexyl, neohexyl, and the like. More preferred are lower alkyl having 1 to 4 carbon atom(s) such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl and t-butyl.
The optionally substituted alkyl includes, for example, the above-mentioned alkyl which may be substituted by one or more substituent(s) which do(es) not influence the reaction. Examples of the substituents include hydroxy; halogen atoms such as fluorine, chlorine, bromine and iodine; amino; nitro; mono- or dialkylamino having 1 to 6 carbon atom(s) such as methylamino, ethylamino, hexylamino, dimethylamino and diethylamino; cyano; cycloalkyl having 3 to 7 carbon atoms such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl; alkoxy having 1 to 6 carbon atom(s) such as methoxy, ethoxy, propoxy, butoxy, pentyloxy and hexyloxy; carboxyl; alkoxycarbonyl having 2 to 6 carbon atoms such as methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl and pentyloxycarbonyl; and the like. Preferred are hydroxy, halogen atom and amino.
The position and number of substituents on alkyl are not particularly limited.
The cycloalkyl ring formed by R1 and R2 in combination together with the adjacent carbon atom is preferably cycloalkyl ring having 3 to 7 carbon atoms, which is exemplified by cyclopropyl ring, cyclobutyl ring, cyclopentyl ring, cyclohexyl ring, cycloheptyl ring, and the like. Preferred is that having 4 to 6 carbon atoms, such as cyclobutyl ring, cyclopentyl ring and cyclohexyl ring.
The chiral amine is that having an asymmetric carbon atom adjacent to amino group, that is, amine having an (R) or (S) configuration. Typical examples include aralkylamine, amino acid derivative and the like.
Examples of aralkylamine include (R)-1-phenylethylamine, (S)-1-phenylethylamine, (R)-1-(1-naphthyl)ethylamine, (S)-1-(1-naphthyl)-ethylamine, (R)-xcex1-phenylglycinol, (S)-xcex1-phenylglycinol, and the like. Preferred is (R)-1-phenylethylamine.
The amino acid derivative includes, for example, amino acids having an asymmetric carbon atom adjacent to amino group, and derivatives thereof. Specific examples include amino acids such as (R)-serine, (S)-serine, (R)-xcex1-phenylglycine and (S)-xcex1-phenylglycine; amino acid derivatives such as (R)-serine methyl ester, (S)-serine methyl ester, (R)-xcex1-phenylglycine methyl ester and (S)-xcex1-phenylglycine methyl ester; and the like. Preferred is (R)-xcex1-phenylglycine.
Aralkylamine residue and amino acid derivative residue respectively mean a group which is other than amino group and which binds to amino group in the above-mentioned aralkylamine and amino acid derivative.
Examples of aryl include phenyl, naphthyl, biphenyl, and the like. Preferred is phenyl.
The optionally substituted aryl includes, for example, the above-mentioned aryl which may be substituted by one or more substituent(s) having no influence on the reaction. Examples of the substituent include those exemplified with respect to the above-mentioned optionally substituted alkyl; alkyl having 1 to 6 carbon atom(s) such as methyl, ethyl, propyl, butyl, pentyl and hexyl; alkenyl having 2 to 6 carbon atoms such as vinyl, allyl, butenyl, pentenyl and hexenyl; acyloxy having 2 to 6 carbon atoms such as acetyloxy, propionyloxy, butyryloxy, pivaloyloxy and hexanoyloxy; and the like. Preferred are alkyl, hydroxy, halogen atom, amino, nitro, alkoxy and acyloxy, and more preferred are alkyl, hydroxy, halogen atom, alkoxy and acyloxy.
While the position and number of substituents on aryl are not particularly limited, preferred are compounds having 1 to 3 substituent(s) and more preferred are compounds having 1 or 2 substituent (s).
The aryl moiety of aralkyl is exemplified by those mentioned above such as phenyl, naphthyl and biphenyl, and the alkyl moiety thereof is exemplified by those mentioned above having 1 to 6 carbon atom(s). The aralkyl is exemplified by benzyl, phenethyl, phenylpropyl, phenylbutyl, phenylhexyl, and the like. Preferred is aralkyl comprising phenyl with C1-C4 alkyl.
The optionally substituted aralkyl is that which may be substituted by one or more substituent(s) which exert(s) no influence on the reaction. Examples of the substituent include those exemplified with respect to the aforementioned optionally substituted aryl; haloalkyl having 1 to 6 carbon atom(s) such as chloromethyl, chloroethyl and chlorobutyl; and the like. Preferred are hydroxy, halogen atom, alkyl, alkoxy, haloalkyl, nitro, acyloxy, amino and cyano. More preferred are halogen atom, alkyl, alkoxy and acyloxy. Specific examples of optionally substituted aralkyl include benzyl, halogen-substituted benzyl, alkyl-substituted benzyl, alkoxy-substituted benzyl, phenethyl, halogen-substituted phenethyl, alkyl-substituted phenethyl, alkoxy-substituted phenethyl, phenylpropyl, halogen-substituted phenylpropyl, alkyl-substituted phenylpropyl, alkoxy-substituted phenylpropyl, and the like. Preferred are benzyl, phenethyl, and the like.
While the position and number of substituents on aryl of the above-mentioned aralkyl are not particularly limited, preferred are compounds having 1 to 3 substituent(s).
Heteroaryl is, for example, pyridyl, pyrimidyl, pyrazinyl, furyl, thienyl, pyrrolyl, imidazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, indolyl, isoindolyl, quinolyl, isoquinolyl, phthalazinyl, naphthyridinyl, quinazolinyl, cinnolinyl or quinoxalinyl, with preference given to quinolyl and isoquinolyl.
The optionally substituted heteroaryl is that which may be substituted by one or more substituent(s) which exert(s) no influence on the reaction. Examples of the substituent include those exemplified with respect to the aforementioned optionally substituted aryl, and the like. Preferred are alkyl, hydroxy, halogen atom, amino, nitro, mono- or dialkylamino, alkoxy, acyloxy, carboxyl and alkoxycarbonyl. More preferred are alkyl, hydroxy, halogen atom, mono- or dialkylamino, alkoxy and acyloxy.
While the position and number of substituents on heteroaryl are not particularly limited, preferred are compounds having 1 to 3 substituent(s), and more preferred are compounds having 1 or 2 substituent(s).
The heteroaryl moiety of the heteroarylalkyl includes, for example, those exemplified above and the alkyl moiety includes, for example, those exemplified above having 1 to 6 carbon atom(s). Specific examples include 2-thienylmethyl, 3-furylmethyl, 4-pyridylmethyl, 2-quinolylmethyl, 3-isoquinolylmethyl, and the like. Preferred is 2-quinolylmethyl.
The optionally substituted heteroarylalkyl is, for example, that which may be substituted by one or more substituent(s) which exert(s) no influence on the reaction. Examples of the substituent include those exemplified with respect to the aforementioned optionally substituted heteroaryl, and the like.
While the position and number of substituents on heteroaryl of the above-mentioned heteroarylalkyl are not particularly limited, preferred are compounds having 1 to 3 substituent(s).
Examples of acyl include saturated aliphatic acyl preferably having 1 to 18 carbon atom(s), such as formyl, acetyl, propionyl, butyryl, isobutyryl, valeryl, isovaleryl, pivaloyl, hexanoyl, lauroyl, myristoyl, palmitoyl and stearoyl; unsaturated aliphatic acyl preferably having 3 to 18 carbon atoms, such as acryloyl, propioloyl, methacryloyl, crotonoyl and oleoyl; aromatic acyl, such as benzoyl, naphthoyl, toluoyl, hydratropoyl, atropoyl and cinnamoyl; heterocyclic acyl, such as furoyl, thenoyl, nicotinoyl and isonicotinoyl; acyl of hydroxy acid or alkoxylic acid, such as glycoloyl, lactoyl, glyceroyl, tropoyl, benziloyl, salicyloyl, anisoyl, vanilloyl, veratroyl, piperonyloyl, protocatechuoyl and galloyl; and the like. Preferred is saturated aliphatic acyl and more preferred are formyl, acetyl, propionyl and butyryl.
The hetero ring to be formed by R6 and R7 together with the adjacent nitrogen atom is, for example, saturated or unsaturated heteroaryl having one or more nitrogen atom(s). Specific examples include imidazolyl, triazolyl, tetrazolyl, pyrrolyl, pyrrolidinyl, imidazolidinyl, hydropyridyl, piperidino, piperazinyl, oxazinyl, morpholino, azepinyl, hydroazepinyl, indolyl, hydroindolyl, isoindolyl, hydroisoindolyl, hydroquinolyl, hydroisoquinolyl, and the like. Preferred are the groups represented by the following formulas 
wherein the broken line may be either double bond or single bond, and more preferred is the group represented by the following formula: 
Said hetero ring may be substituted by halogen atom, alkyl having 1 to 6 carbon atom(s), alkenyl having 2 to 6 carbon atoms, alkoxy having 1 to 6 carbon atom(s), amino, alkoxycarbonyl having 2 to 6 carbon atoms, carboxamide, or alkyl-substituted carbamoyl wherein the alkyl moiety has 1 to 6 carbon atom(s).
While the position and number of substituents on hetero ring are not particularly limited, preferred are compounds having 1 to 3, more preferably 1 or 2, substituent(s).
The halogen atom as the substituent for hetero ring includes, for example, fluorine, chlorine, bromine and iodine.
The alkyl as the substituent for hetero ring includes, for example, the aforementioned ones having 1 to 6 carbon atom(s).
The alkenyl as the substituent for hetero ring includes, for example, linear or branched alkenyl preferably having 2 to 6 carbon atoms, which is exemplified by vinyl, allyl, crotyl, 2-pentenyl, 3-pentenyl, 2-hexenyl and 3-hexenyl. More preferred are those having 2 to 4 carbon atoms such as vinyl, allyl and crotyl.
The alkoxy as the substituent for hetero ring includes, for example, linear or branched alkoxy preferably having 1 to 6 carbon atom(s), which is exemplified by methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, s-butoxy, t-butoxy, pentyloxy, isopentyloxy, neopentyloxy, hexyloxy, and the like. More preferred are those having 1 to 4 carbon atom(s) such as methoxy, ethoxy, propoxy, isopropoxy and butoxy, with further preference given to those having 1 or 2 carbon atom(s) such as methoxy and ethoxy.
The alkoxycarbonyl as the substituent for hetero ring includes, for example, alkoxycarbonyl preferably having 2 to 6 carbon atoms, which is exemplified by the above-mentioned alkoxy having 1 to 5 carbon atom(s) with carbonyl group, and the like.
The alkyl-substituted carbamoyl as the substituent for hetero ring includes, for example, those wherein the alkyl moiety preferably has 1 to 6 carbon atom(s), which is exemplified by N-methylcarbamoyl, N-ethylcarbamoyl, N-propylcarbamoyl, N-t-butylcarbamoyl, N-pentylcarbamoyl, N-hexylcarbamoyl, and the like. Preferred is N-t-butylcarbamoyl.
The substituent (Z group) which functions as a leaving group together with oxygen atom includes, for example, as a group joining with oxygen atom (leaving group: OZ group), sulfonic acid derivatives such as tosyloxy (p-toluenesulfonyloxy), brosyloxy (p-bromobenzene-sulfonyloxy), mesyloxy (methanesulfonyloxy), benzenesulfonyloxy, camphorsulfonyloxy and trifyloxy (trifluoromethanesulfonyloxy). Preferred is mesyloxy (methanesulfonyloxy).
The reactive carboxylic acid derivative having R4 includes, for example, acid halides (e.g., R4COCl and R4COBr), acid anhydrides (e.g. (R4CO)2O) and mixed acid anhydrides (e.g., R4COOCOtxe2x80x94Bu and R4COOCOOEt) of carboxylic acid having R4 (R4COOH). Preferred are acid halides and more preferred is R4COCl.
Examples of Lewis acid include titanium chloride, tin chloride, zinc chloride, zinc bromide, zinc iodide, magnesium chloride, titanium alkoxide, boron bromide, boron chloride, boron fluoride, boron trifluoride-diethyl ether complex, aluminum chloride, aluminum bromide, thionyl chloride, phosphorus oxychloride, phosphorus chloride, trimethylsilyl chloride, trimethylsilyl iodide, trimethylsilyl trifluoromethanesulfonate, and the like. Preferred are thionyl chloride, tin chloride and boron trifluoride-diethyl ether complex, with more preference given to boron trifluoride-diethyl ether complex.
Examples of salts include, but not limited to, alkali metal salts such as sodium salt, potassium salt and cesium salt; alkaline earth metal salts such as calcium salt and magnesium salt; organic amine salts such as triethylamine salt, pyridine salt, picoline salt, ethanolamine salt, triethanolamine salt, dicyclohexylamine salt and N,Nxe2x80x2-dibenzylethylenediamine salt; inorganic acid salts such as hydrochloride, hydrobromide, sulfate and phosphate; organic acid salts such as formate, acetate, trifluoroacetate, maleate and tartrate; sulfonates such as methanesulfonate, benzenesulfonate and p-toluenesulfonate; and amino acid salts such as arginine, aspartate and glutamate.
The present invention encompasses various isomers of respective compounds.
The method for producing compound [XV] from (z)-2-butene-1,4-diol which is used as a starting compound, that is, the method for producing compounds inclusive of the above-mentioned final objective compound [XVI] useful as an HIV protease inhibitor is described in detail in the following. 
wherein R1, R2, R3, R4, R5, R6, R7, R8 and Z are as defined above, and X is halogen atom, alkoxycarbonyloxy, acyloxy or xe2x80x94OCOR4 wherein R4 is as defined above.
Examples of halogen atom include those mentioned above. Alkoxycarbonyloxy preferably has 2 to 6 carbon atoms and is exemplified by methoxycarbonyloxy, ethoxycarbonyloxy, propoxy-carbonyloxy, butoxycarbonyloxy, and the like. Acyloxy preferably has 2 to 6 carbon atoms and is exemplified by acetyloxy, propionyloxy, valeryloxy, pivaloyloxy, and the like.
Step (1): Protection of Diol
The reaction per se is known wherein (z)-2-butene-1,4-diol [I] is reacted with an acetalating agent or a ketalating agent without solvent or in a suitable solvent, in the presence of a dehydrating agent or a suitable catalyst such as acid, thereby to protect hydroxyl groups and produce compound [II].
Examples of the acetalating agent and ketalating agent include carbonyl compounds such as formaldehyde, acetaldehyde, benzaldehyde, acetone, diethyl ketone, methyl ethyl ketone, acetophenone, cyclopentanone and cyclohexanone; gem-dialkoxy compounds such as dimethoxymethane, 1,1-dimethoxyacetaldehyde, benzaldehydodimethyl-acetal, 2,2-dimethoxypropane and cyclohexanone dimethylacetal; vinyl ether compounds such as methyl vinyl ether, ethyl vinyl ether, 2-methoxypropene, 2-ethoxypropene and 1-methoxycyclohexene; and the like. Preferred are gem-dialkoxy compounds with more preference given to 2,2-dimethoxypropane.
The catalyst is appropriately selected according to the kind of acetalating agent and ketalating agent. Suitable catalyst includes, for example, inorganic acids such as sulfuric acid, hydrochloric acid and nitric acid; and organic acids such as acetic acid, trifluoroacetic acid, methanesulfonic acid, p-toluenesulfonic acid, benzenesulfonic acid and camphorsulfonic acid. Preferred are organic acids with more preference given to p-toluenesulfonic acid.
Examples of the dehydrating agent include phosphorus pentoxide, molecular sieves, phosphorus pentachloride, and the like. Preferred are molecular sieves.
The solvent is appropriately selected according to the kind of acetalating agent and ketalating agent. Suitable solvent includes, for example, hydrocarbon solvents such as benzene, toluene, hexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; ester solvents such as ethyl acetate, methyl acetate and butyl acetate; and polar solvents such as N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile and acetone, with preference given to hydrocarbon solvents and more preference given to a reaction without solvent.
The reaction (refluxing) temperature is suitably 0-200xc2x0 C., preferably 80-160xc2x0 C.
The compound [II] can be used directly in the next step without isolation.
Step (2): Epoxidation with Oxidizing Agent
This step comprises epoxidation of compound [II] without solvent or in a suitable solvent using an oxidizing agent to give compound [III]. Like Step (1), this reaction per se is known (see U.S. Pat. No. 4,439,613).
As the oxidizing agent, inorganic oxidizing agents such as hydrogen peroxide, Oxon(trademark); and organic oxidizing agents such as metachloroperbenzoic acid, peracetic acid and t-butylhydro-peroxide can be used. Preferred are inorganic oxidizing agents and more preferred is hydrogen peroxide. In this case, sodium hydroxide, or sodium hydroxide and disodium hydrogenphosphate in combination are desirably co-used for smooth progress of the reaction.
The solvent is appropriately selected according to the kind of oxidizing agent. Suitable solvents include, for example, alcohol solvents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol and t-butyl alcohol; hydrocarbon solvents such as benzene, toluene, hexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; ester solvents such as ethyl acetate, methyl acetate and butyl acetate; polar solvents such as N,N-dimethylformamide, acetonitrile, acetone, formic acid, acetic acid and water; and mixed solvents thereof. Preferred are alcohol solvents and more preferred is a mixed solvent of methanol, acetonitrile and water.
While the reaction temperature varies depending on the oxidizing conditions, it is suitably 0-150xc2x0 C. and preferably 50-100xc2x0 C. The reaction time is preferably 3 to 8 hours.
The compound [III] can be used directly in the next step without isolation.
Step (3): Epoxy Ring-opening Reaction with Chiral Amine
This step comprises epoxy ring-opening of compound [III] with chiral amine [IV] of the formula : R3xe2x80x94NH2 wherein R3 is as defined above, in a suitable solvent or without solvent, and subjecting the mixture of isomers thus produced to crystallization (e.g. recrystallization) to give an optically pure compound [V] or an enantiomer thereof.
As mentioned above, the chiral amine includes, for example, aralkylamines represented by (R)-1-phenylethylamine, (S)-1-phenylethylamine, (R)-1-(1-naphthyl)ethylamine, (S)-1-(1-naphthyl)-ethylamine, (R)-xcex1-phenylglycinol and (S)-xcex1-phenylglycinol; amino acids such as (R)-serine, (S)-serine, (R)-xcex1-phenylglycine and (S)-xcex1-phenylglycine; and amino acid derivatives such as (R)-serine methyl ester, (S)-serine methyl ester, (R)-xcex1-phenylglycine methyl ester and (S)-xcex1-phenylglycine methyl ester, with preference given to chiral aralkylamine and more preference given to chiral 1-phenylethylamine.
By appropriately selecting the chiral amine, a compound [V] or an enantiomer of compound [V] can be obtained.
Suitable solvents to be used for the reaction include, for example, alcohol solvents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol and t-butyl alcohol; hydrocarbon solvents such as benzene, toluene, hexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; polar solvents such as N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, acetone and water; and mixed solvents thereof. Preferred are alcohol solvents and more preferred is isopropyl alcohol.
The reaction temperature is suitably 0-150xc2x0 C. and preferably 50-100xc2x0 C. The reaction time is preferably 20 to 30 hours.
Suitable solvents to be used for crystallization include, for example, alcohol solvents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol and t-butyl alcohol; hydrocarbon solvents such as benzene, toluene, hexane, heptane, methylcyclohexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; ester solvents such as ethyl acetate, methyl acetate and butyl acetate; polar solvents such as N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, acetone and water; and mixed solvents thereof. Preferred are hydrocarbon solvents and a mixed solvent of hydrocarbon solvent and alcohol solvent and more preferred is a mixed solvent of hexane or heptane, and isopropyl alcohol.
Step (4): Removal of Chiral Element
This step comprises removing chiral element (R3) under suitable conditions from the compound [V] or an enantiomer thereof obtained in Step (3) to give a chiral compound [VI] or an enantiomer thereof.
The conditions of removal are appropriately determined according to the kind of chiral element. For example, when R3 is 1-phenylethyl, the chiral element can be removed by catalytic reduction in a suitable solvent in the presence of a suitable catalyst such as palladium hydroxide, and hydrogen source.
In this case, suitable catalyst includes, for example, palladium catalysts (e.g., palladium hydroxide-carbon, palladium-carbon and palladium-alumina), platinum catalysts (e.g., platinum oxide), rhodium catalysts (e.g., rhodium-alumina) and ruthenium catalysts (e.g., ruthenium-alumina). Preferred are to palladium catalysts with more preference given to palladium hydroxide-carbon.
Examples of the hydrogen source include hydrogen gas, ammonium formate, formic acid, cyclohexadiene, and the like. Preferred is hydrogen gas.
Suitable solvent includes, for example, alcohol solvents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol and t-butyl alcohol; hydrocarbon solvents such as benzene, toluene, hexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; ester solvents such as ethyl acetate, methyl acetate and butyl acetate; polar solvents such as N,N-dimethylformamide, formic acid, acetic acid and water; and mixed solvents thereof. Preferred are alcohol solvents, polar solvents and a mixed solvent of alcohol solvent and polar solvent, and more preferred is a mixed solvent of isopropyl alcohol, acetic acid and water.
The reaction temperature is suitably 0-100xc2x0 C. and preferably 20-60xc2x0 C. The reaction time is preferably 5 to 20 hours.
Step (5): Acylation of Amino Group
This step comprises acylation of amino group of compound [VI] or an enantiomer thereof using an acylating agent [VII] comprising a reactive carboxylic acid derivative having R4 group, in a suitable solvent in the presence of a suitable base, to give compound [VIII] or an enantiomer thereof.
Examples of R4 of the reactive carboxylic acid derivative having R4 group, which is used as an acylating agent, include optionally substituted alkyl such as methyl, ethyl, propyl, butyl, s-butyl and t-butyl; optionally substituted aryl such as phenyl, 4-tolyl, 3-tolyl, 2-tolyl, 3-acetoxy-2-methylphenyl, 3-hydroxy-2-methylphenyl, 1-naphthyl and 2-naphthyl; optionally substituted heteroaryl such as 2-thienyl, 3-thienyl, 2-furyl, 3-furyl, 2-pyridyl, 3-pyridyl and 4-pyridyl; optionally substituted aralkyl such as benzyl, phenethyl, 1-naphthylmethyl and 2-naphthylmethyl; optionally substituted heteroarylalkyl such as 2-thienylmethyl, 3-thienylmethyl, 2-furylmethyl, 3-furylmethyl, 2-pyridylmethyl, 3-pyridylmethyl and 4-pyridylmethyl; and the like. Preferred are 3-acetoxy-2-methylphenyl and 3-hydroxy-2-methylphenyl.
The reactive carboxylic acid derivative having R4 group is appropriately selected according to the substitution mode of the desired final product, and, for example, acid halides, acid anhydrides and mixed acid anhydrides of carboxylic acid (R4COOH) having R4 group may be used.
Examples of acid halides of carboxylic acid (R4COOH) having R4 group include R4COCl, R4COBr, and the like. Examples of acid anhydride include (R4CO)2O, and the like. Examples of mixed acid anhydride include R4COOCOtxe2x80x94Bu, R4COOCOOEt, and the like.
Examples of suitable base include organic base such as pyridine, lutidine, picoline, triethylamine, diisopropylethylamine, dimethylaminopyridine, DBU (1,8-diazabicyclo[5.4.0]-7-undecene) and DBN (1,5-diazabicyclo[4.3.0]-5-nonene); and inorganic base such as lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium hydrogencarbonate, potassium hydrogencarbonate, sodium carbonate and potassium carbonate. Preferred are inorganic bases, particularly sodium hydrogencarbonate.
Suitable solvent includes, for example, alcohol solvents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol and t-butyl alcohol; hydrocarbon solvents such as benzene, toluene, hexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; ester solvents such as ethyl acetate, methyl acetate and butyl acetate; polar solvents such as N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, acetone and water; and mixed solvents thereof. Preferred is a heterogeneous solvent of Schotten-Baumann comprising halogen solvent and water, and more preferred is a solvent comprising dichloromethane and water.
The reaction temperature is suitably 0-100xc2x0 C. and preferably 10-40xc2x0 C. The reaction time is preferably 1 to 5 hours.
The compound [VIII] can be used directly as an extracted solution in the next step without isolation.
Step (6): Sulfonylation of Hydroxy
This step comprises introduction of a substituent Z which functions, together with an oxygen atom, as a leaving group wherein the hydroxy of the compound [VIII] or an enantiomer thereof is sulfonylated in a suitable solvent in the presence of a suitable base using a suitable sulfonylating agent to give a compound [IX] or an enantiomer thereof.
Examples of suitable sulfonylating agent include sulfonyl chloride such as methanesulfonyl chloride, benzenesulfonyl chloride, toluenesulfonyl chloride and camphorsulfonyl chloride; sulfonic anhydride such as methanesulfonic anhydride and trifluoromethane-sulfonic anhydride; and the like. Preferred is sulfonyl chloride, and more preferred is methanesulfonyl chloride.
Suitable base includes, for example, organic bases such as pyridine, lutidine, picoline, triethylamine, diisopropylethylamine, dimethylaminopyridine, DBU and DBN. Preferred are pyridine and triethylamine with more preference given to triethylamine.
Suitable solvent includes, for example, hydrocarbon solvents such as benzene, toluene, hexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; ester solvents such as ethyl acetate, methyl acetate and butyl acetate; polar solvents such as N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile and acetone; and mixed solvents thereof. Preferred are halogen solvents and more preferred is dichloromethane.
The reaction temperature is suitably xe2x88x9210-30xc2x0 C. and preferably 0-20xc2x0 C. The reaction time is preferably 1 to 10 hours.
The compound [IX] can be used directly as an extracted solution in the next step without isolation.
Step (7): Formation of Oxazoline Ring
This step comprises treating compound [IX] or an enantiomer thereof with a suitable Lewis acid in a suitable solvent, thereby simultaneously deprotecting 1,3-dioxepane ring and forming oxazoline ring, to give a compound [X] or an enantiomer thereof wherein R5 is hydrogen atom. After the reaction, the obtained compound is treated with a suitable acylating agent in the same reaction vessel to convert hydroxy to acyl to give a stabler compound [X] or an enantiomer thereof wherein R5 is acyl.
Examples of Lewis acid include, as mentioned above, titanium chloride, tin chloride, zinc chloride, zinc bromide, zinc iodide, magnesium chloride, titanium alkoxide, boron bromide, boron chloride, boron fluoride, boron trifluoride-diethyl ether complex, aluminum chloride, aluminum bromide, thionyl chloride, phosphorus oxychloride, phosphorus chloride, trimethylsilyl chloride, trimethylsilyl iodide, trimethylsilyl trifluoromethanesulfonate, and the like. Preferred are thionyl chloride, tin chloride and boron trifluoride-diethyl ether complex. More preferred is boron trifluoride-diethyl ether complex.
Suitable solvent includes, for example, hydrocarbon solvents such as benzene, toluene, hexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; ester solvents such as ethyl acetate, methyl acetate and butyl acetate; polar solvents such as N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile and acetone; and mixed solvents thereof. Preferred are halogen solvents and more preferred is dichloromethane.
Examples of suitable acylating agent include acid halides such as acetyl chloride, benzoyl chloride and pivaloyl chloride; acid anhydrides such as acetic anhydride, benzoic anhydride and pivalic anhydride; and the like. Preferred are acid anhydrides, more preferably acetic anhydride.
The reaction temperature is suitably 0-100xc2x0 C. and preferably 10-40xc2x0 C. The reaction time is preferably 1 to 50 hours.
The reaction is terminated by adding an aqueous solution of a suitable base. Examples of the suitable base include inorganic bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogencarbonate and potassium hydrogencarbonate; and organic bases such as N,N-dimethylethanolamine and N-methylmorpholine, which are selected as appropriate according to the kind of Lewis acid to be used. For example, when boron trifluoride-diethyl ether complex is used, N-methylmorpholine is preferably used.
The compound [X] can be used directly as a concentration residue in the next step without isolation.
Step (8): Epoxidation
This step comprises treating compound [X] or an enantiomer thereof with a suitable base in a suitable solvent to give compound [XI] or an enantiomer thereof.
Suitable base includes, for example, inorganic bases such as sodium hydride, potassium hydride, lithium hydride, lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogencarbonate and calcium carbonate; and organic bases such as pyridine, triethylamine, diisopropyl ethylamine, lutidine, DBU, DBN, alkoxides (e.g., sodium methoxide, sodium ethoxide and potassium t-butoxide), and alkali metal amides (e.g., lithium amide, sodium amide, potassium amide and lithium diisopropylamide), with preference given to inorganic bases and more preference given to potassium hydroxide and potassium carbonate.
Suitable solvent includes, for example, alcohol solvents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol and t-butyl alcohol; hydrocarbon solvents such as benzene, toluene, hexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; polar solvents such as N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, acetone and water; and mixed solvents thereof. Preferred is a mixed solvent of alcohol solvent and water, and more preferred is a mixed solvent of water and isopropyl alcohol or methanol.
The reaction temperature is suitably 0-100xc2x0 C. and preferably 0-60xc2x0 C. The reaction time is preferably 1 to 10 hours.
The compound [XI] can be used as an intermediate in a reaction mixture without isolation, and so-called one-pot reaction can be carried out in the next step.
Step (9): Epoxy Ring Opening with Amine
This step comprises treating compound [XI] or an enantiomer thereof with amine [XII] in a suitable solvent to open epoxy ring, thereby to give a compound [XIII] or an enantiomer thereof.
As the amine, any amine can be used as long as it has at least one hydrogen atom on nitrogen, and examples thereof include ammonia, methylamine, ethylamine, propylamine, isopropylamine, aniline, anisidine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, methylethylamine, methylisopropylamine, methylaniline, pyrrolidine, piperidine, decahydroisoquinoline, (3S, 4aS, 8aS)-decahydroisoquinoline-3-carboxylic acid t-butylamide, and the like.
Suitable solvent includes, for example, alcohol solvents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol and t-butyl alcohol; hydrocarbon solvents such as benzene, toluene, hexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; polar solvents such as N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, acetone and water; and mixed solvents thereof. Preferred is a mixed solvent of alcohol solvent and water, and more preferred is a mixed solvent of water and isopropyl alcohol or methanol.
The reaction temperature is suitably 0-100xc2x0 C. and preferably 20-70xc2x0 C. The reaction time is preferably 1 to 10 hours.
The compound [XIII] can be obtained all at once by reacting compound [X] which is a starting compound in the previous Step (8), compound [XII] and a suitable base.
Examples of the suitable base include inorganic bases such as sodium hydride, potassium hydride, lithium hydride, lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogencarbonate and calcium carbonate; and organic bases such as pyridine, triethylamine, diisopropyl ethylamine, lutidine, DBU, DBN, alkoxides (e.g., sodium methoxide, sodium ethoxide and potassium t-butoxide), and alkali metal amides (e.g., lithium amide, sodium amide, potassium amide and lithium diisopropylamide). Preferred are inorganic bases with more preference given to potassium carbonate.
Suitable solvent includes, for example, alcohol solvents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol and t-butyl alcohol; hydrocarbon solvents such as benzene, toluene, hexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; polar solvents such as N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, acetone and water; and mixed solvents thereof. Preferred is a mixed solvent of alcohol solvent and water, and more preferred is a mixed solvent of methanol and water.
The reaction temperature is suitably 0-100xc2x0 C. and preferably 20-70xc2x0 C.
Step (10): Oxazoline Ring Opening with Thiol
This step comprises reacting compound [XIII] or an enantiomer thereof with thiol [XIV] in a suitable solvent in the presence of a base, thereby simultaneously opening oxazoline ring and thiolating to give a compound [XV] or an enantiomer thereof.
Examples of the thiol include alkylmercaptans such as methylmercaptan, ethylmercaptan, propylmercaptan, isopropylmercaptan, butylmercaptan, s-butylmercaptan and t-butylmercaptan; aralkylmercaptans such as benzylmercaptan; arylmercaptans such as thiophenol and toluenethiol; and the like. Preferred are to arylmercaptans, more preferably thiophenol.
Suitable base includes, for example, inorganic bases such as sodium hydride, potassium hydride, lithium hydride, lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate and calcium carbonate; and organic bases such as pyridine, triethylamine, diisopropylethylamine, lutidine, DBU, DBN, alkoxides (e.g., sodium methoxide, sodium ethoxide and potassium t-butoxide), and alkali metal amides (e.g., lithium amide, sodium amide, potassium amide and lithium diisopropylamide), with preference given to triethylamine and potassium hydrogencarbonate.
Suitable solvent includes, for example, alcohol solvents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, t-butyl alcohol and ethylene glycol; hydrocarbon solvents such as benzene, toluene, hexane and xylene; ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran and diglyme; halogen solvents such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane; polar solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, acetonitrile and acetone; ketone solvents such as methyl isobutyl ketone, diethyl ketone and methyl ethyl ketone; and mixed solvents thereof. Preferred are polar solvents and ketone solvents, and more preferred are N,N-dimethylformamide and methyl isobutyl ketone.
The reaction temperature is suitably 0-150xc2x0 C. and preferably 80-130xc2x0 C. The reaction time is preferably 1 to 30 hours.
The enantiomers of the above-mentioned compound [XV] and various intermediates can be obtained by the same reactions as above using an enantiomer of compound [V] obtained in Step (3).
The compound [XV], various intermediates and enantiomers thereof can be obtained at optional purity by appropriately applying separation and purification conventionally known, such as concentration, extraction, chromatography, reprecipitation and recrystallization.
The salts of the above-mentioned compound [XV], various intermediates and various isomers thereof can be produced by a known method.
The present invention is described in detail by way of illustrative Examples in the following, to which the invention is not limited.
Examples are shown in a schematic flow in the following. 
wherein Ph is phenyl, Ac is acetyl, Me is methyl and Bu-t is t-butyl. Reference Example 1:3-Acetoxy-2-methyl benzoic acid
3-Nitro-2-methyl benzoic acid (90.5 g, 0.500 mol) was dissolved in 1.0 mol/L aqueous solution (500 ml) of sodium hydroxide. 10% Palladium-carbon (4.5 g) was added and the mixture was stirred under a hydrogen atmosphere (2-3 atm) for 9 hours at 40xc2x0 C. The catalyst was filtered off and conc. sulfuric acid (94.0 ml) was added under ice-cooling. An aqueous solution of sodium nitrite (35.0 g, 0.500 mol/150 ml) was added over one hour while stirring the mixture at not more than 6xc2x0 C., and after the dropwise addition, the mixture was heated at 65xc2x0 C. for 1.5 hours. The inner temperature rose to 57xc2x0 C. in an hour. The reaction mixture was cooled to room temperature, and saturated brine (300 ml) was added. The mixture was extracted with ethyl acetate (700 ml). The organic layer was washed with saturated brine (200 ml) and dried over magnesium sulfate. The solvent was distilled away to give 3-hydroxy-2-methyl benzoic acid as a pale brown solid.
This substance was dissolved in pyridine (500 ml), and acetic anhydride (100 ml) was added at room temperature, which was followed by stirring at room temperature for 3.5 hours. Ethanol (100 ml) which was kept at not more than 10xc2x0 C. was added to the reaction mixture, and the mixture was stirred for another hour at room temperature. The mixture was concentrated to give a brown oil. The oil was dissolved in ethyl acetate (800 ml) and washed successively with 1N hydrochloric acid (500 ml) and saturated brine (300 ml). Magnesium sulfate and active charcoal (4.00 g) were added to the organic layer, and the mixture was stirred for 30 minutes. The insoluble matter was filtered off and the filtrate was concentrated to dryness. Acetic acid in this product was removed by azeotropy using toluene (400 ml), and the residue was washed with toluene (450 ml) to give 3-acetoxy-2-methyl benzoic acid (70.1 g, yield 72%) as colorless crystals, melting point 146-148xc2x0 C.
1H-NMR (CDCl3, 300 MHz) xcex4: 7.95 (dd, 1H,J=1.5,7.3 Hz), 7.30 (t, 1H, J=7.7 Hz), 7.24 (dd, 1H,J=1.5,8.1 Hz), 2.46 (s,3H), 2.36 (s,3H) IR (KBr): 2984, 2816, 1766, 1687, 1460, 1311, 1279, 1211, 1039, 930, 766, 752 cmxe2x88x921 
Elemental Analysis (C10H10O4): Calculated: C, 61.85;H, 5.19. Found: C, 61.91;H, 4.94.